sed -n '\@.*/Users/\([^/]*\)/.*@ s//\1/p' text.file
The -n suppresses output unless data is printed explicitly. The \@ notation replaces the search character (default /) with @. Then the search pattern looks for /Users/ followed by a sequence of non-slashes and a slash, capturing the non-slashes (user name); it matches everything else on the line too (the .* at beginning and end). The s//\1/p` command replaces what was matched (the whole line) with what was captured (the user name), and prints the information.
Alternatively, you can use a backslash-slash sequence to match the slashes in the data:
sed -n '/.*\/Users\/\([^/]*\)\/.*/ s//\1/p' text.file
You do not need a backslash before the slash in the character class, but the other backslashes are needed. If you were unwise enough to have a user name d\lee and you included a backslash in the character class, you would not see the name d\lee in the output.